• The return of spontaneous circulation (ROSC), defined as the development of a palpable pulse of any duration.
  

• Maximum duration of ROSC (the duration of the longest episode of sustained pulse return)
  
• ROSC duration by survival analysis
  
• Survival to hospital admission
  
• Survival to hospital discharge
  
• Length of hospital stay
  
• Non-sinus tachyarrhythmias in the first 24 hours after study drug administration
  
• Seizures in the first 24 hours after study drug administration
  
• Neurologic outcome
  
• Proportion of subjects receiving one versus two doses of study drug
  
• Proportion of subjects achieving ROSC with initial-rhythm bradyasystole versus bradyasystole which developed after paramedic arrival.
  

Out-of-hospital cardiac arrest treated by emergency medical services has an estimated incidence of 54.99 per 100,000 person years, which translates to some 155,000 episodes annually in the United States. Bradyasystole is the first recorded rhythm in up to 52 percent of cardiac arrests, and many additional patients with an initial cardiac arrest rhythm of ventricular fibrillation deteriorate to bradyasystole after defibrillation efforts. Survival to hospital discharge occurs in less than 3 percent of patients presenting with bradyasystole; however, due to its frequency, this rhythm accounts for over 17 percent of all cardiac arrest survivors. As a result, even a small improvement in survival from bradyasystolic cardiac arrest would result in thousands of lives saved annually.

Adenosine is an endogenous purine nucleoside that depresses the sinoatrial node, blocks atrioventricular conduction, inhibits the pacemaker activity of the His-Purkinje system and attenuates the effects of catecholamines. Since adenosine is produced and released by myocardial cells during ischemia and hypoxia, it may be a reversible factor in the etiology or perpetuation of bradyasystole. Aminophylline is a competitive antagonist of adenosine. The use of aminophylline for bradycardia and heart block has been described, and a number of anecdotal reports and small studies have been published on the use of aminophylline in cardiac arrest. We undertook this study to evaluate the effect of aminophylline during cardiopulmonary resuscitation (CPR) of patients with out-of-hospital bradyasystolic cardiac arrest unresponsive to initial therapy.